DENVER, Colorado (CNN) -- On a historic night for America, Barack Obama secured the Democratic Party's nomination for president and emerged for the first time on stage in Denver with running mate Sen. Joe Biden.

Obama on Wednesday officially became the first African American to lead a major party ticket.

Delegates cried and cheered as former rival Sen. Hillary Clinton motioned to cut the roll call vote short, saying "Let's declare together with one voice right here, right now, that Barack Obama is our candidate and he will be our president."

The Democrats jumped to their feet as they made history with Obama as their leader. Outside the hall, Republican leaders also hailed the achievement.

On Thursday, the 45th anniversary of Martin Luther King Jr.'s "I have a dream" speech, in the culmination of the Democratic National Convention, Obama will address an estimated 70,000 people at Invesco field in Denver. Read more about the historic anniversary

"This is something people like me have been waiting for for days, weeks. Years," said Howard Hemsley, an African-American delegate from New York. "He's going to the White House. He's going to be our next president." iReport.com: "Never thought I'd see this day"

"Now, Sen. Obama's life is a 21st-century incarnation of the old-fashioned American dream. His achievements are proof of our continuing progress toward the more perfect union of our founders' dreams," he said. "Barack Obama will lead us away from the division and fear of the last eight years back to unity and hope." Watch the sights and sounds of the convention events »

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President Clinton and Biden, two of the party's elder statesmen, lavished praise upon the newly crowned nominee and did their best to paint Republican rival Sen. John McCain as a candidate who would lead the country down a dangerous path.

Clinton cast Obama as the safe pick, and the only one who could bring about change. He sought to put to rest the main criticism of Obama -- that he does not have the experience to lead. Watch Clinton wow the Democrats »

Obama's perceived weakness compared to McCain on foreign policy and national security issues has been of concern to Democratic strategists, especially since Russia's conflict with Georgia intensified this month.

According to a new CNN/Opinion Research Corp. poll, 78 percent of registered voters said they believe McCain can handle the responsibilities of commander in chief, compared to 58 percent for Obama.

"And here's what I have to say about that. Everything I learned in my eight years as president, and in the work I have done since in America and across the globe, has convinced me that Barack Obama is the man for this job."

The ex-president had been one of the most vocal critics of Obama during the protracted primary season. Republicans have used the Clintons' earlier criticism of Obama's experience in their attacks on the Democratic presidential nominee.

Going into the convention, there were still a lot of questions about whether the Clintons were ready to embrace Obama following the bruising primary battle.

Clinton seemed to change that narrative as he declared his support for Obama.

David Gergen, a CNN senior political analyst who worked in the Clinton administration, said the speech was "the most effective and the most important speech Bill Clinton has delivered since he left the White House." View an analysis of day 3 »

Continuing criticism leveled by Clinton and other speakers this week, Biden took to the stage and delivered an assault on Republican policies.

"As we gather here tonight, our country is less secure and more isolated than at any time in recent history. The Bush-McCain foreign policy has dug us into a very deep hole, with very few friends to help us climb out," he said.

Biden rattled off a list of McCain's positions on issues ranging from taxes to alternative energy, repeatedly saying: "That's not change -- that's more of the same." Read more about Biden's attacks

Biden, chairman of the Senate Foreign Relations Committee, is widely believed to have been chosen for the Democratic presidential ticket based on his foreign policy credentials. Watch Biden accept the nomination »

The six-term senator pointed to his friendship with McCain, but said "I profoundly disagree with the direction that John wants to take the country."